Vala VAPI file is generated for current GADBC 1.0 API version.

It is disable by default, but recommended to be enable when
a development package is distributed.

This commit force a 1.0 API versioning, replacing the old one
where 0 were used for GIR API version (gir_version), so now
shows '1.0' instead of '0.0'.

Also examples are provided for C and Vala.

* New Statement.execute_query() for queries without results or ignoring them
* New Statement.execute_reader() for queries returning results and converting
them to GArrowRecordBatchReader

Above methods allows to ignore extrange API current in Statement.execute()
when using on Vala